This invention relates to an interpolymer of olefinically unsaturated carboxylic acids or anhydrides and a polymeric surface active agent (or surfactant), having a linear block or random comb configuration which provides a steric stabilizing component to the interpolymer and produces a polymer which is easier to disperse and handle.
Carboxyl containing polymers of vinyl or vinylidene monomers containing at least one terminal CH.sub.2 .dbd.C&lt; group are well known. Such polymers may be homopolymers of unsaturated polymerizable carboxylic acids, such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid and the like; or copolymers of said acid or anhydride monomers with (meth)acrylate esters, (meth)acrylamides, olefins, maleic anhydrides, vinyl esters, vinyl ethers, and styrenics; or copolymers with other vinyl or vinylidene monomers. Often, copolymers of these acids are cross-linked with small amounts of cross-linking agents. These materials are normally prepared by polymerization with a free radical catalyst in an organic medium in a closed vessel or autoclave equipped with stirring. During the course of such polymerizations, the polymer begins to precipitate from the solution as it is formed and flocculates and forms aggregates. The precipitated polymer is then recovered and dried to remove residual solvent. The polymer, which is now in a powder form, is used usually by dispersing it in water, neutralizing it, and adding it to a liquid to use its thickening ability. Such polymers are disclosed in U.S. Pat. Nos. 2,798,053; 3,915,921; 3,940,351; 4,062,817; 4,066,583; and 4,267,103.
Surfactants have been employed in the manufacture of carboxyl containing polymers because, in their manufacture, the aggregation of the polymer can interfere with the polymerization reaction by retarding access of the monomer to free radicals and by interfering with the removal of the heat produced by the polymerization. Further, the precipitated polymer forms a slurry in the solvent which becomes extremely thick, resulting in ineffective mixing and fouling on reactor surfaces. In response to these problems, and to increase the usually low total solids to a range of about 8 to 17 weight percent and increase productivity, a variety of surfactants have been employed.
For example, U.S. Pat. No. 4,375,533 to Park et al. discloses a process for overcoming some of the above problems, in which the polymerization of acrylic acid, and optional comonomers, in an organic media, is characterized by the use of nonionic surface active agents having a hydrophobe to lipophobe balance (HLB) values between 1 and about 10. U.S. Pat. No. 4,419,502, to Sehm, disclosed a process for the polymerization of acrylic acid and optional comonomers in the presence of a nonionic surface active agent selected from polyoxyethylene alkyl ethers and polyoxyethylene sorbitol esters and having an HLB value greater than 12. U.S. Pat. No. 4,420,596, to Lochhead et al., disclosed a process for polymerizing carboxylic acids in mineral spirits, employing nonionic surface active agents having HLB values less than 10. U.S. Pat. No. 4,526,937 to Hsu teaches the polymerization of acrylic acid in an organic solvent with a free radical catalyst, using nonionic block copolymers of propylene oxide and ethylene oxide to minimize undesirable flocculation and agglomeration. U.S. Pat. No. 4,692,502 to Uebele et al. teaches a process for polymerizing acrylic acid in an organic media with a free radical catalyst and at least one oil-soluble ionic surfactant selected from an anionic formula, a cationic formula, or an amphoteric formula to achieve reduced polymer build-up in the reactor and provide a more desirable particle size for the precipitated polymer.